1. Field of the Invention
The present invention generally relates to printers such as those which are commonly used in conjunction with a computer terminal. More particularly, the present invention relates to a shielding device for keeping printing media particles away from the printhead and other moving parts of the printer that such particles or accumulations of particles can disrupt.
2. Description of the Related Art
One of the problems with the use of computer-type printers is paper dust and accumulations of paper dust or the interference such can cause to the printhead and other moving parts within the printer. For example, in an impact-hammer type printhead, dust can accumulate on the hammerheads and degrade the print quality. The problem is increased when the printer uses continuous, fan-fold paper which has perforations between each sheet. If the paper is of the type which uses sprocket wheel paper advance drive, sprocket holes and perforations also exist along tear-off strips on each side of each sheet, adding further sources of unwanted paper dust.
In fact, experiments by the inventors indicate that the primary source of paper dust is the sprocket holes themselves. In other words, as the sprocket is inserted and withdrawn during paper advance, the contact between the sprocket and the perimeter of each sprocket hole creates paper dust.
Paper dust is particularly a nuisance to a thermal ink jet printhead which has a set of tiny orifices designed to eject boiled ink vapor droplets. A single particle of paper dust may be sufficient to clog such an orifice. A general description of such ink jet technology can be found, for example, in the Hewlett Packard Journal, Volume 36, Number 5, May 1985.
WALLACE ET AL., U.S. Pat. No. 4,411,706, present a method and apparatus for keeping dust away from ink jet printhead orifices by using an air counterflow technique. This concept requires complicated, costly mechanism design.
Hence, there is a need for a simple means for preventing paper dust from interfering with the operational parts of a printer.